1. Technical Field
The present invention is directed toward a safety device for oxygen delivery tubing, and more particularly toward a method and apparatus for extinguishing combustion within combustible tubing.
2. Background Art
It is a standard therapy for patients suffering from acute respiratory disorders to provide supplemental oxygen. A conventional oxygen delivery assembly includes a patient interface such as a nasal cannula, face mask, endotracheal fitting or the like with the supplemental oxygen being delivered to these patient interfaces from an oxygen supply by flexible plastic tubing, such as a polyvinyl chloride (PVC) tubing. In some instances, the oxygen delivery tubing is only several feet long and the oxygen supply is ambulatory. In other instances, the oxygen supply is stationary and the tubing is on the order of 50-100 feet long to enable the patient to move around a defined area while receiving supplemental oxygen.
Standard PVC oxygen tubing cannot sustain combustion under typical ambient conditions (i.e., oxygen concentration of 22%). However, if ignited in the presence of enriched oxygen (greater than 22%) the PVC tubing will burn aggressively. The PVC tubing can be ignited from exposure to an electrical short, cooking element, open flames such as candles and the like. However, it is believed that the most common cause of ignition of oxygen delivery PVC tubing is exposure to flames and sparks associated with smoking. Once the PVC tubing is ignited, the flame initially starts as an external fire and then moves to the tubing interior and migrates rapidly upstream toward the oxygen source. Should the migration of the combustion be arrested by encountering a non-combustible fitting, such as a metal connector, combustion will intensify within the PVC tubing adjacent the connector, eventually burning through the PVC tubing and causing a radical external flame which presents a severe risk of spreading the fire beyond the tubing. Under standard flow rates of 2-6 liter per minute and pressures of 4-7 psi, the point of combustion migrates at approximately one foot per second within the tubing. The precise rate of migration of the flame is dependent on the rate of oxygen flow, with the point of combustion migrating more quickly as the rate of oxygen flow increases.
The fire hazard of standard oxygen delivery assemblies in clinical settings is significant, but is typically mitigated by supervision of the patients, mandatory smoke detectors, fire alarms and other institutional safety practices such as strictly enforced no smoking policies. However, in jurisdictions not having these safety controls, the potential for catastrophic fires is considerably enhanced.
In the last several years, in an effort to control spiraling healthcare costs, considerable efforts have been dedicated to treating patients outside of clinical settings such as the patient's homes. Typically these alternative care locations do not include the many safeguards of the clinical setting. In addition, private homes can present an abundance of hazards such as substandard electrical appliances and cooking facilities that are not generally present in the clinical setting. Moreover, outside of the clinical setting there are fewer restrictions on the patient's behavior. It is much easier for the patient to engage in potentially hazardous activities, such as smoking. Thus, in these settings the potential for catastrophic fires is enhanced. Unfortunately, the prior art has done little to minimizes the serious fire risk at the source. Thus, patients, who are often ill-equipped to do so, are left to combat a fire after it has spread from the oxygen delivery assembly.
Mims et al., U.S. Pat. No. 5,392,825, is directed to a pressure regulator with an integral flashback arrester. The flashback arrester consists of a check valve and a porous metal flashback arrester manufactured from powered stainless steel sintered to form an elongate cup-like structure. In normal operation, combustible gas from a pressurized gas source flows in a downstream direction through the check valve. The flow of the gas unseats a disk within the check valve. In the event of a flashback, increased pressure will occur upstream of the check valve, thus biasing the disk to a seated position, thereby preventing flow of the flashback into the regulator and temporarily interrupting flow of the combustible gas. Mims further teaches that should the flashback pass through the check valve, the porous metal flashback arrester should extinguish the flashback.
The structure of Mims is complicated and, therefore, relatively expensive which would inhibit its widespread use as part of an oxygen delivery assembly. In addition, Mims does not intend to permanently halt the flow of combustible gas once a flashback occurs. Rather, once the flashback is arrested, flow of the combustible gas would begin again which could create a renewed hazard.
Anderson, U.S. Pat. No. 5,676,712, is also directed to a flashback protection apparatus. Anderson describes an apparatus for stopping a flashback of flame in a combustible gas conduit by using a "bolus" or bulk volume of non-combustible gas introduced into the conduit to halt the progress of the flashback. Anderson suffers the same shortfall of Mims in that it is a complicated, expensive structure. Furthermore, Anderson does not provide for permanently cutting off the flow of combustible gas.
The present invention is directed toward overcoming one or more of the problems discussed above.